And what is calomel? Mercurous chloride, used to treat malaria, yellow fever and dysentery and, in a preparation called worm chocolate or worm candy, gastrointestinal parasites. People who were given large doses for long periods suffered from excessive salivation, gum inflammation, loosening of the teeth, gastrointestinal upset, and an ashen appearance, as well as troubling neurologic symptoms, such as arm and facial tremors, ataxia (an inability to coordinate voluntary muscular movements symptomatic of a central nervous system disorder), and erethism (unusual timidity and personality change). Mercury as medicine!